Shraddha rituals consist of following main activities –
Pindadan is the offering of rice, cow's milk, Ghee, sugar and honey in form of Pinda (rounded heap of the offering) to the ancestors. Pandadan should be done with whole-heartedness, devotion, sentiments and respect to the deceased soul to fulfil it.
Tarpan is the offering of the water mixed with black sesame (तिल), Barley (जौं), Kusha grass (कुशा) and white flours. It is believed that ancestors are appeased by the process of Tarpan.
Feeding the Brahmin is must to complete the Shraddha ritual. Offering to the crows are also made before food is offered to the Brahmin.
Pitru Paksha is the period of fifteen lunar days when Hindus pay homage to their ancestors, especially through food offerings. Each lunar month is divided into two equal Paksha which are known as Shukla Paksha and Krishna Paksha. Each Paksha consists of fifteen lunar days.
According to North Indian Purnimant Calendar, fifteen days period during Krishna Paksha of Ashwin month is known as Pitru Paksha. But according to South Indian Amavasyant Calendar, fifteen days period during Krishna Paksha of Bhadrapada month is known as Pitru Paksha. It is interesting to note that it is just nomenclature of lunar months which differs and both North Indians and South Indians perform Shraddha rituals on similar days.
Many sources include Bhadrapada Purnima which usually falls one day before Pitru Paksha into fifteen days period of Pitru Paksha. Bhadrapada Purnima which is also known as Proshthapadi Purnima is an auspicious day to perform Shraddha rituals but it is not part of Pitru Paksha. It should be noted that Mahalaya Shraddha for those who died on Purnima Tithi is done on Amavasya Shraddha Tithi during Pitru Paksha and not on Bhadrapada Purnima.
Pitru Paksha starts one or two days after Ganesh Visarjan. Pitru Paksha is also known as Mahalaya Paksha. The last day of Pitru Paksha is known as Sarvapitri Amavasya or Mahalaya Amavasya. This is the most significant day of Pitru Paksha. If the death date of the deceased person in the family is not known then his or her Shraddha can be performed on Sarvapitri Amavasya.
In West Bengal Mahalaya Amavasya marks the beginning of Durga Puja festivity. It is believed that Goddess Durga was descended on the Earth on this day.
According to Garuda Purana, after thirteen days of the death soul starts its journey for Yamapuri and it takes seventeen days to reach there.
The soul travels through Yamapuri for another eleven months and only in twelfth month it reaches to the court of Yamaraj. During the period of eleven months it has no access to the food and the water. It is believed that Pindadan and Tarpan done by the son and family members satisfy the hunger and the thirst of the soul during its journey till it reaches the court of the Yamaraj.
Hence Shraddha rituals are considered very important during first year of the death.